Insulated electrical lead



Patented Aug. 12, 1952 INSULATED ELECTRICAL LEAD ChristianDantsizen,Schenectady, N. Y., assignor to General Electric Company, a corporationof N ew. York Application May 24, 1949, Serial No. 94,970

4 Claims.

This invention relates to electrical leads and methods for constructingthem. More particularly, the invention relates to electrical conductorsarranged singly or in groups of two or more within an outer sheathwiththe conductors separated from each other and from the sheath byelectrical insulating material. The invention relates also to theconstruction. of barriers for electrical conductors and cables forpreventing the how of insulating compound or other fluids betweenseparate sections of a conductor or cable.

An object of my invention is the provision of an insulating medium forone or more conductors within a sheath, which completely'fills theintervening space between conductors and between conductors and sheathso as to prevent pockets of air or other vapors which might result in abreakdown under electrical stress.

A further object of the invention is the provision, for an electricallead assembly having one or more conductors Within a sheath, ofaninsulating medium which tightly engages the conductors and the sheathto prevent the entry into the assembly'of moisture, vapor, gases or thelike which might cause'a breakdown under electrical stress.

A further object of my invention'is to provide an electricallyinsulative'material which is suitable for tightly engaging an electricalconductor or conductors and a surrounding sheath or other outer memberto form a barrier to prevent the flow of insulating compound or otherfluid along the conductors.

A still further object of the invention is to provide an insulatedelectrical lead or group of leads which, in addition to performing theusual current carrying functions, can be used to seal the opening in acontainer through which the leads are brought into the container inorder to prevent the escape of the contents of the container through theopening.

In carrying out my invention in one form, I place around a copper wire alayer of a material of that class of materials which, upon be-- ingdeformed while cold, return to substantially their original shape whensubsequentlyheated to the proper temperature. The copper wire and thelayer of material aroundit are placed within a steel sheath. The entireassembly is then swaged to reduceits cross sectional dimensions, afterwhich it is heated to cause the intervening layer of material to attemptto regainits original shape. In this manner; the intervening layer ofmaterial is caused tightly to engage the center copper conductor and theouter steel sheath and seal the electrical lead, thus formed, againstmoisture and other foreign materials.

For a clearer and more complete understanding of my invention, referenceshould be had to the accompanying drawing, Fig. 1 of which is alongitudinal sectional view illustrating one step in the construction ofan electrical lead in accordance with my invention; Fig. 2 is asectional view of this lead in finished form; Figs. 3 and dillustrate astep in the construction of abarrier or seal in accordancewith amodification of my invention; and Fig. 5 is a sectional viewillustrating an additional step in the construction of such a barrier.

Inthe preferred embodiment of my invention illustrated by Figs. 1 and 2,an electrical conductor which may be copper wire of circular crosssection is represented by the numeral 1. An outer tubular sheath whichmay be of steel or other malleable material having sufiicient tensilestrength is represented by the numeral 2. Between conductor I and sheath2 is a layer of electrically insulative material 3.

Layer 3 may be composed of any of the class of materials, includingpolymerized tetrafiuorethylene, which have the characteristic ofreturning to substantially their original shape when heated, afterhaving been deformed while cold. In the case of polymerizedtetrafiuorethylene, for example, if it is deformed while cold and thenheated at 356 to 400 degrees centigrade for a short time, it will regainsubstantially its original shape, if it is not restrained while beingheated. Other examples of materials having. this characteristic arepolymerized monochlorotrifluorethylene and polymerized methylmethacrylate. The former returns to substantially its original shape,after having been deformed while unheated, when it is heated atapproximately 200 degrees centigrade for a short time. The latter tendsto return to its original shape, or reform, when heated at temperaturesless than degrees centigrade.

In the construction of a typical insulated electrical lead in accordancewith my invention, I first provide a cylindrical piece of polymerizedtetrafiuorethylene having a length and diameter equal to the length anddiameter of layer 3 in Fig. 1. I then drill a hole through the piece ofpolymerized tetrafluorethylene along the center line thereof, into whichconductor I will fit snugly. Conductor I, which is of circular copperwire in this instance, may then be sandblasted to improve the subsequentadherence between the wire and the surrounding insulating material,after which the conductor l is inserted into the hole in the polymerizedtetrafiuorethylene. The member 3 of polymerized tetrafiuorethylene isthen inserted into sheath 2, the inside diameter of which is such that avery close fit results between sheath 2 and insulating layer 3.

The insulated lead assembly is then swaged and reduced in diameter,being simultaneously elongated, until it is of the form illustrated inFig. 2. The entire assembly is then heated at 350 to 400 degreescentigrade for a short timei During the heating operation, thepolymerized tetrafluorethylene attempts to shrink in a directionparallel to the center line of the assembly and return to its originaldiameter, which causes it to expand with considerable force against thesheath 2. The sheath prevents outward expansion so the pressure isreflected against the sandblasted or knurled surface of conductor I. Inthis manner, the existence of vapor pockets in the insulated electricallead is precluded and a tight seal is provided between the conductor andthe insulation and between the insulation and the outer sheath whichprevents the subsequent entrance of any fluid, vapor, or other foreignmaterial.

A modification of my invention in which the characteristics ofpolymerized tetrafluorethylene and other similar substances are utilizedto create a sealed barrier around one or more electrical conductors isillustrated in Figs. 3, 4 and 5. In this modification, a cylinder ofpolymerized tetrafluorethylene is swaged or otherwise subjected topressure while cold to reduce its diameter and elongate it. Theresulting elongated cylinder of reduced diameter is illustrated in Figs.3 and 4. One or more holes, depending upon the number of electricalconductors desired, are then drilled longitudinally through the cylinderand electrical conductors are inserted in the holes. Fig. 3 illustratessuch a cylinder 4 in which a single conductor 5 has been inserted,

whileFig. 4 illustrates a similar cylinder 6 in which three electricalconductors l, 8, and 9 have been inserted.

The cylinder 4 or 6 of polymerized tetrafiuorethylene is then insertedin a steel shell ll] of circular cross section. In this instance,cylinder 4, having a single conductor, is used for purposes ofillustration. A longitudinal sectional view of shell 10, with cylinder 4and conductor 5 assembled therein, is shown in Fig. 5. It can be seen inthis figure that the inner surface of this typical outer shell is flaredfrom both ends toward the center, which forms an annular space H betweencylinder 4 and shell l0. After cylinder 4 is placed within shell H], theentire assembly is heated at 350 to 400 degrees centigrade for a shorttime. This causes the cylinder 4 of polymerized tetrafiuorethylene toexpand against the side walls of the steel shell, filling the annularspace i l, and against the conductor 5, thus forming a tight sealbetween insulation 4 and both conductor 5 and shell Hi.

It is readily apparent that an insulated electrical lead forming asealed barrier, as illustrated in Fig. 5, has many uses. For example, itmay be used as a termination or connection for a conventional fluidfilled electrical cable to prevent the escape of the insulating fluid orthe flow of the insulating fluid from one section of such a cable toanother. An additional use is to permit the introduction of electricalenergy into a container through an opening and simultaneously provide aseal for the opening. In the latter instance, it has a great advantageover other sealing means now in use because it allows the use of copperconductors. With other sealing means, such as glass, less eflicientconductors of metals other than copper must be used, because of thenecessity of matching the coefficient of expansion of the conductor asclosely as possible to that of the glass.- By utilizing my invention,copper can be successfully used for the electrical conductors. I havefound, for example, that a sealed electrical lead constructed inaccordance with my invention, utilizing a copper conductor, polymerizedtetrafiuorethylene as the electrical insulating material, and a steelsheath, and assembled in the manner illustrated by Fig. 5, willsuccessfully withstand an air pressure greater than 80 lbs. per sq.inch.

While I have illustrated and described one preferred embodiment of myinvention, together with one modification thereof, many additionalmodifications will occur to those skilled in the art and, therefore, itshould be understood that I intend to cover by the appended claims anysuch modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method of forming an electrical lead which comprises covering anelectrical conductor with a layer of a material of the class which afterbeing deformed while cold returns to substantially its original shapewhen subsequently heated, applying a sheath of malleable material on theouter surface of said material, swaging the assembly thus formed toreduce the cross sectional area thereof, and then heating said materialto cause it to attempt to return to its original shape whereby saidmaterial tightly engages said conductor and said sheath.

2. The method of forming an insulated electrical lead which comprisesplacing around an electrically conductive wire a layer of a material ofthe class including polymerized tetrafluorethylene, which tends toregain its original shape upon being heated at a suitable temperatureafter having been deformed while cold, placing said wire and said layerof material within an outer sheath strong enough to prevent deformationof the sheath when the layer of material is subsequently heated, swagingsaid sheath to reduce the cross sectional area of the assembled sheath,wire and intermediate layer of material, and heating said assembledgroup to cause said layer of material to attempt to regain its originalshape whereby said material tightly engages said wire and said sheath.

3. The method of forming an insulated electrical lead which comprisesboring a hole along the axis of a cylinder of a material of the classincluding polymerized tetrafluorethylene, which tends to regain itsoriginal shape upon being heated at a suitable temperature after havingbeen deformed while cold, inserting an electrically conducting wire insaid hole, placing said material and said wire into a tubular sheath,swaging the assembly thus formed to reduce the crosssectional area ofthe said wire, said material, and said sheath, heating said assembly tocause said material to attempt to expand radially to regain its originalshape whereby said material tightly engages said wire and said sheath.

4. The method of forming an insulated electrical lead which comprisesboring a hole along the axis of a cylinder of polymerizedtetrafiuorethylene, which tends to regain its original shape upon beingheated at a suitable temperature after having been deformed while cold,inserting a sand-blasted electrically conducting wire in said hole,placing said cylinder and said wire into a tubular sheath, swaging theassembly thus formed to reduce the cross-sectional area of said wire,said cylinder, and said sheath, heating said assembly to from 350 C. to400 C. to cause said cylinder to attempt to expand radially to regainits original shape whereby said cylinder tightly engages said wire andsaid sheath.

CHRISTIAN DANTSIZEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,233,807 Head July 1'7, 19172,225,298 Cook Dec. 17, 1940 2,341,235 Palmer Feb. 8, 1944 2,405,057Rosenstein July 30, 1946 2,431,085 Shelmerdine Nov. 13, 1947 2,454,525Bondon Nov. 23, 1948 2,466,271 Pfleumer Apr. 5, 1949 2,469,416 SmyersMay 10, 1949

1. THE METHOD OF FORMING AN ELECTRICAL LEAD WHICH COMPRISES COVERING ANELECTRICAL CONDUCTOR WITH A LAYER OF A MATERIAL OF THE CLASS WHICH AFTERBEING DEFORMED WHILE COLD RETURNS TO SUBSTANTIALLY ITS ORIGINAL SHAPEWHEN SUBSEQUENTLY HEATED, APPLYING A SHEATH OF MALLEABLE MATERIAL ON THEOUTER SURFACE OF SAID MATERIAL, SWAGING THE ASSEMBLY THUS FORMED TOREDUCE THE CROSS SECTIONAL AREA THEREOF, AND THEN HEATING SAID MATERIALTO CAUSE IT TO ATTEMPT TO RETURN TO ITS ORIGINAL SHAPE WHEREBY SAIDMATERIAL TIGHTLY ENGAGES SAID CONDUCTOR AND SAID SHEATH.